The present invention relates to a process for shielding the launch ends of laser catheters used in photoablation of deposits in the vascular systems of the human body.
Laser catheters used in the medical field to recanalize clogged arteries have specific requirements. For example, load capacity and durability of the system must be able to accommodate associated threshold luminations. Launching of high energy, pulsed laser radiation at the proximal end of the catheter is an especially weak point in such systems system, often self-destructing under usual operating conditions, thereby curtailing the service life of the device.
For purposes of photoablation, launch side luminations of 20 J/cm.sup.2 are necessary. Short, high-energy laser pulses in one or more optical fibers must be launched in the spectral range between 240-3000 nm. The threshold luminations required for photoablation to recanalize vessels, especially in the case of calcified occlusions, must be high enough to ablate organic material.
The launching surface of a single or multifiber laser catheter can change due to unavoidable movement of the laser beam. It is not possible to completely eliminate irradiation over the effective cross-section of the fiber or fiber bundle at the front sides of the launch surface In addition, the cross-section of the beam cannot be adapted easily to the cross-section of a multifiber catheter, causing unavoidable partial irradiation.
The materials used to hold the light fibers according to the prior art do not withstand incident lumination, resulting in ablation of the holding material at the launch side and early destruction of the catheter. For example, ablation of metal holding material leads to metal particle deposits on the launch surface of the fibers, indirectly causing destruction of the fiber. The use of standard plastics as holding materials does not overcome the shortcomings of the prior art because decomposition products of the plastic are deposited on the fiber end surface, resulting in loss of the setting and fiber destruction. Such deterioration poses significant risk to successful recanalization.